Threat is a possible security danger in the computing system. It might exploit a vulnerability to breach the security. So, it causes possible harm. There are four categories of threats:

• Interception
• Interruption
• Fabrication
• Modification

Interception means gaining access to unauthorized service or data in a computer system. Illegal copying is an appropriate example. Interruption makes the system resources unavailable or destroyed, for example, intentional file corruption. Fabrication is related to including the unwanted additional data. Modification alters the original specification of the system to break using unauthorized access.